The Section on Developmental Gastroenterology and Nutrition was established to study cellular differentiation and migration. The desirable model for this study is the intestinal epithelium because in a short period of time (48 hours), the undifferentiated crypt cell undergoes proliferation, migration, and differentiation. This orderly sequence of events in the jejunum of the rat provides a convenient investigative model. Differentiation gradients from crypt to villus are biochemically demonstrated by increasing levels of disaccharidases and ornithine carbamyl transferase. Thymidine kinase levels to evaluate cellular proliferation demonstrate increased activity at the undifferentiated cell level, but are not specific for intestinal cells. We are seeking by he application of biochemical, immunocHemical and cytochemical techniques to define the role of actin, myosin and fibronectin in intestinal cell migration and adhesion. In addition we are continuing our efforts to understand the cntrol of sucrose/ isomaltase syntesis and the mode of incorporation o the complex into the intestinal brush-border-membrane.